Loans and Leases Receivable and Allowance for Loan and Lease Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 16,599	$ 15,551
Non-Accrual	16,265	27,494
Current	7,287,302	7,073,879
Loans and lease receivable, gross	7,338,555	7,138,498
Loans and leases receivable, at amortized cost or lower of cost or market	$ 7,338,555	7,138,498
Delinquent period	30 days
Due days for loan payments	90 days
Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	$ 18,389	21,574
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14,656	13,363
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,943	2,188
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,662	0
Non-Accrual	0	1,155
Current	2,294,926	3,282,452
Loans and lease receivable, gross	2,300,244	3,285,297
Multi-family | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	1,656	1,690
Multi-family | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,662	0
Multi-family | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	860	1,914
Non-Accrual	5,314	17,764
Current	1,881,586	1,353,586
Loans and lease receivable, gross	1,888,134	1,373,800
Commercial and industrial | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	374	536
Commercial and industrial | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	860	1,914
Commercial and industrial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	686	193
Non-Accrual	2,068	1,037
Current	465,934	567,809
Loans and lease receivable, gross	475,465	577,477
Commercial real estate owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	6,777	8,438
Commercial real estate owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	686	193
Commercial real estate owner occupied | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,190
Non-Accrual	83	129
Current	1,264,361	1,119,443
Loans and lease receivable, gross	1,268,557	1,125,106
Commercial real estate non-owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	4,113	4,344
Commercial real estate non-owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,190
Commercial real estate non-owner occupied | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Non-Accrual	0	0
Current	61,200	56,491
Loans and lease receivable, gross	61,200	56,491
Construction | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	0	0
Construction | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,485	5,940
Non-Accrual	6,093	5,605
Current	616,533	550,679
Loans and lease receivable, gross	628,786	566,561
Residential real estate | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	3,675	4,337
Residential real estate | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,485	5,940
Residential real estate | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,096	6,114
Non-Accrual	1,567	1,693
Current	64,362	69,916
Loans and lease receivable, gross	72,616	79,731
Cash	24	500
Manufactured housing | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	1,591	2,008
Manufactured housing | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,153	3,926
Manufactured housing | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,943	2,188
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,810	200
Non-Accrual	1,140	111
Current	638,400	73,503
Loans and lease receivable, gross	643,553	74,035
Other consumer | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	203	221
Other consumer | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,810	200
Other consumer | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0